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Conclusion:
According to Ibn al-Haytham:
From the experimental examination of the conditions of the diameters on the board and of the objects fixed on them at points other than the middle, it is manifest that every object lying on the common axis and perceived by means of the radial axis will appear in its own place, where perception of it is acquired with one eye and one visual axis or with both eyes and both axis. It is manifest, moreover, that every object perceived by one eye and by means of the radial axis, but which does not lie on the common axis, will appear at a place closer to the common axis than its true place. The same also holds for what is perceived through rays other than the axis; for if sight perceives an object as it is, and the form of that object occurs at a single place in the cavity of the common nerve, so that the parts of it are joined together in the way they are in the object.79
In reviewing Ibn al-Haytham's visual physiology with the advantage of almost a thousand years' hindsight, his achievements are still impressive. Virtually single-handedly he created the foundations of modern physiological optics, an accomplishment which is astonishing considering the severe technological limitations of his period. Much more important than these achievements, however, is his remarkable insight into the method of modern scientific inquiry. His experiments on the rectilinear propagation of light document this new approach. Furthermore, his belief that experimental observation alone is the final arbiter of the truth of scientific theory is his most original contribution. For example, when he observed that objects are seen both by perpendicular and by incidental rays, he modified his view on the central role of perpendicular rays in vision even though it meant abandoning his theory of an upright image in the eye. It is as the pioneer of empiricism that Ibn al-Haytham made his most significant contributions to the neurosciences.80
According to Sabra, Ibn al-Haytham was the first and foremost mathematician who was contributing to what he consciously conceived as a "physico-mathematical" project; and while his discussions of visual illusions may be said to have epistemological implications, his treatment of them is clearly the work of one who wrote as an experimental psychologist and not as an epistemologist.81 Sabra concludes:
The experimental orientation of Ibn al-Haytham's concepts and procedures is unmistakable. With the addition of measurement, Book III would have been indistinguishable in character from a modern book in experimental psychology.
82
If Ibn al-Haytham had lived for another ten years, he may have written an eighth and ninth chapter of The Book of Optics titled "Psychophysics" and "Experimental Psychology," combining psychology with physics, or the mind with the body.
Khaleefa and Manaa83 from the University of Bahrain have carried out an empirical study regarding Ibn al-Haytham's previously summarized experiments. Their study discovered the existence of an i'tibar which they titled "Ibn al-Haytham Scale for the Error of Vision" (IHSEV), which dates back to the eleventh century. The study shows that Boring, the well-known historian of psychology, had attempted to conquer by his treatise "A History of Experimental Psychology," a theoretical Mount Everest. Boring asks: How did experimental psychology - scientific psychology - come into being and what is it's nature? First, there is the Renaissance, and then the emergence of science, with the names of Copernicus (1543), Kepler (1609), Galileo (1638), and finally Newton (1687) standing out. Vision was the best understood of the five senses. Newton's Optics (1704) is no doubt responsible for it. Not only did this book and subsequent work of the physicists render a fairly complete knowledge of the laws of refraction and of optical instruments available for application to the problem of the eye, but it is also true that the Optics, especially in respect to color, contributed some incidental psychological information.84
The Khaleefa and Manaa study shows that Ibn al-Haytham actually put forward the basis of the experimental method in his well-known encyclopedia The Book of Optics and that numerous Latin translations of the book were to have a profound influence on the history of science up until the seventeenth century. In addition to this, the study presents the contribution of psychophysicists in the West such as Weber, Fechner, and Helmoholtz, who engaged in one important aspect of their early experimentation with vision. As early as the eleventh century, Ibn al-Haytham was the first scientist who experimentally investigated and formulated a theory of vision, visual perception, and the error of vision. Their empirical study shows that Ibn al-Haytham rigorously followed the scientific experimental method in his marvelous study of the error of vision. The renewed IHSEV has been applied to a sample of 235 participants from Bahrain, who were selected with respect to gender, age, and educational level. Some procedures were adapted in the application of the renewed scale. The most remarkable finding of Khaleefa and Manaa's study is the concordance of their findings with Ibn al-Haytham's i'tibar (method) by 78 percent. According to the complexity of the study as based on Ibn al-Hayham's Optics, their findings are explained from a number of dimensions, including visual geometry, physiological physics, and psychology.
The question in the present study is this: Who is the "founder" of psychophysics and experimental psychology? Boring described "founding" in these terms:
When the central ideas are all born, some promoter takes them in hand, organizes them, adding whatever else seems to be essential, publishes and advertises them, insists upon them, and in short "founds" a school.85
Thus, "founding" is quite different from originating, though we need not make the distinction a disparaging one. Both originators and founders are essential to the formation of a science, as indispensable as are the architect and the builder in constructing a house.86 Taha concluded, "It can safely be said that Ibn al-Haytham is the founder of the psychology of vision87and "modern psychophysics.88It is our conclusion that Ibn al-Haytham deserves the full title of Founder of Psychophysics as well as Founder of Experimental Psychology. The Book of Optics by Ibn al-Haytham in the first half of the eleventh century, and not the Elements of Psychophysics by Fechner in the nineteenth century, marks the official "founding" of psychology because it provides not only new concepts and theories, but new methods of measurement in psychology.
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